Bond enthalpies Flashcards
You can get information about the strength of a chemical bond from its what?
bond enthalpy. bond enthalpies tell you how much energy is needed to break different bonds.
When energy is needed to break bonds it is what?
endothermic eg. H-H = 2H ΔH= +436KJmol-1
definition of bond enthalpy?
the enthalpy change that takes place when breaking 1 mole of a given bond in the molecules of a gaseous species.
what is the average bond enthalpy?
the average enthalpy change that takes place when breaking 1 mole of a given type of bond in the molecules of a gaseous species.
Explain the type of reactions during a reaction and when it occurs
when bonds are broken, it is an endothermic process as it requires energy. then when the bonds are formed energy is released so it is exothermic
calculation of whether its exo or endo
bond enthalpies of broken bonds - bonds made
When is a bond enthalpy change exothermic?
when the bonds that are formed are stronger than the bonds that are broken
when is a bond enthalpy change endothermic?
the bonds that are formed are weaker than the bonds that are broken
What is hess’ law?
if a reaction can take place by more than 1 route and the initial and final conditions are the same, the total enthalpy change is the same for each route. A+B=C
why is it not always possible to measure the enthalpy change of a reaction directly?
a high activation energy, a slow reaction rate, more than one reaction taking place
which way do the arrows point for combustion and formation?
down for combustion and up for formation
